Diagnostic device for internal-combustion engine

A diagnostic device for a direct injection internal combustion engine that comprises a fuel injection valve that injects fuel into a combustion chamber of the internal combustion engine, a fuel rail that stores fuel that is to be injected through the fuel injection valve, a fuel pump that discharges fuel to the fuel rail, a fuel pressure sensor that detects a fuel pressure within the fuel rail, and an air-fuel ratio sensor that detects an air-fuel ratio within exhaust gas discharged from the internal combustion engine, the diagnostic device comprising:

• injection amount computation means that computes an injection amount of the fuel injection valve based on an operation state of the internal combustion engine;
• injection correction amount computation means that computes an injection correction amount for the injection amount so as to bring the detected air-fuel ratio to a target air-fuel ratio;
• fuel injection valve control means that corrects the injection amount based on the injection correction amount, and controls the fuel injection valve so as to inject fuel in the corrected injection amount;
• discharge amount computation means that computes a discharge amount of the fuel pump based on the corrected injection amount;
• discharge correction amount computation means that computes a discharge correction amount for the discharge amount so as to bring the detected fuel pressure to a target fuel pressure;
• fuel pump control means that corrects the discharge amount based on the discharge correction amount, and controls the fuel pump so as to discharge fuel in the corrected discharge amount;
• fuel pressure value shifting means that performs, when the injection correction amount deviates from a predetermined range, a shift in a fuel pressure value of the detected fuel pressure until the injection correction amount converges to a predetermined amount within the predetermined range, and that performs, when the injection correction amount deviates from the predetermined range to an increase-side, a shift in the detected fuel pressure value to decrease the fuel pressure value, thereby converging the injection correction amount to the predetermined amount within the predetermined range, and performs, when the injection correction amount deviates from the predetermined range to a decrease-side, a shift in the detected fuel pressure value to increase the fuel pressure value, thereby converging the injection correction amount to the predetermined amount within the predetermined range;
• and
• anomaly determination means that determines which of the fuel pump, the fuel injection valve, and the fuel pressure sensor has an anomaly based on the discharge correction amount before the fuel pressure value shift starts and after the fuel pressure value shift ends and on the injection correction amount before the fuel pressure value shift starts.